a{
    text-decoration: none;
    color:#333;
}
.layout-footer {
    /*（1）固定定位*/
    position:       ;
    z-index: 9999;
    /*（2）（3）左边距离0px，底部距离0px*/
    left:   ;
    bottom:     ;
    /*（4）（5）实现flex布局，主轴对齐方式是两端对齐，项目之间的间隔都相等。*/
    display:     ;
    justify-content:     ;
    width: 100%;
    height: 50px;
    border-top: 1px solid gainsboro;
    color: black;
    text-align: center;
    background-color: #f2f2f2;
}
 
.bottom_nav {
    width: 25%;
    line-height: 50px;
}
.layout-submenu{
    position: fixed;
    height: 80px;
    width: 25%;
    margin-left: -1px;
    z-index: 9999;
    bottom: 50px;
    border: 1px solid gainsboro;
    text-align: center;
    background-color: white;
    display: none;
}
.sub_menu{
    line-height: 40px;
    vertical-align: middle;
}
.layout-footer .bottom_nav:hover{
    border-left: 1px solid gainsboro;
    border-right: 1px solid gainsboro;
}
.layout-footer .bottom_nav:hover .layout-submenu{
    display: block;
 
}
